1. Field of the Invention
The present invention relates to apparatus for collecting samples of drill cuttings and more particularly to such apparatus which collects such samples from a flow of falling drill cuttings.
2. Setting of the Invention
Exploratory wells are drilled to evaluate penetrated rock formations for producible hydrocarbons. In drilling such wells (and in drilling production wells), circulation fluid is pumped down a string of drill pipe and through a drill bit at the lower end thereof. Such fluid thereafter circulates upwardly in the annulus between the drill pipe and the wellbore and thus flushes drill cuttings, such including drilled rock grains and fragments, from the wellbore.
In the usual operation, the drill cuttings are separated from the circulation fluid at the surface of the wellbore. The circulation fluid is thereafter recirculated through the drill string. Typically, such separation is done by what is referred to in the industry as a shale shaker. The shale shaker comprises one or more vibrating screens. Fluid containing the drill cuttings is poured onto the screen(s) which permit the fluid to pass therethrough for recirculation. The screen(s) vibrate the drill cuttings off one end thereof. The drill cuttings are disposed of by burial on land or put in a barge when drilling offshore.
Samples of drill cuttings which are separated from circulation fluid as described above are examined by geologists to evaluate the penetrated rock formations. Such examination is particularly important in connection with exploratory wells which are drilled for the purpose of determining the nature of the formation. It is important to collect samples from all penetrated depths so that the nature of the formations from the surface of the well to the bottom of the bore may be accurately determined. The importance of such samples are increased when, after drilling is complete, a wireline log cannot be acquired or is of poor quality because of a damaged bore. In such cases, the cutting samples and related hydrocarbon records are the only results to show for the expense of drilling the well.
In the past, drill cuttings samples were collected by placing a container in the flow of drill cuttings which falls from the shale shaker. The container is periodically emptied and collected samples are examined. Such prior art sample collectors suffer from several disadvantages. First, the container in which the samples are accumulated may fill to the top and overflow. Drill cuttings falling from the shale shaker when the container is full are not sampled and the record for such drill cuttings is lost. This is especially true in the case of a drilling operation which is drilling at a fairly rapid rate and is thus generating a high volume of drill cuttings per unit time.
Loss of drill cutting samples may also occur when fluids are accidentally introduced into the container collecting the samples. Such may occur as a result of a blinded shaker screen; i.e., the screen becomes clogged and permits circulation fluid to flow with the drill cuttings into the container. Samples may also be lost as a result of water from a hose, which is used to clean the shale shaker, entering the container. In addition, heavy rain and, in offshore drilling operations, waves may introduce water into the container, thus greatly reducing or destroying the information obtainable from the samples. There exists a need for a drill cuttings sample collector which can collect samples at different selected rates.
There also exists a need for a drill cuttings sample collector which prevents unwanted fluids from entering the collector.